Semiconductor light emitting devices that emit light in the infrared region have a wide field of application such as environmental measurement. Among them, semiconductor light emitting devices that emit coherent light, such as a quantum cascade laser, are small and highly convenient, and enable high-accuracy measurement.
For example, a quantum cascade laser that emits infrared light with a wavelength of 4 to 10 μm includes an active layer including quantum wells in which GaInAs and AlInAs are alternately stacked, and has a structure in which an InP cladding layer surrounds the active layer.
On the other hand, in a wavelength region with wavelengths longer than 10 μm, there is light absorption due to lattice vibrations (phonons) of InP, and the InP cladding layer absorbs the light emitted from the active layer. Consequently, the light emitting efficiency decreases, and it is difficult to obtain a high-power quantum cascade laser. Thus, a high-power semiconductor light emitting device that emits light is required in the far-infrared region with wavelengths longer than 10 μm.